The present invention relates to an improved process for producing pigmented powder coating materials using an agent for improving pigment dispersion.
The preparation of powder coating materials by extrusion in corotating twin-screw extruders or single-screw compounders is widely known. Powder coating materials are composed of                binders, such as polyester resins, for example, which are crosslinked using, for example, epoxides, triglycidyl isocyanurate (TGIC), β-hydroxyalkylamine, or blocked isocyanates (uretdiones)        pigments and fillers, except in the case of clearcoats. The pigments must have appropriately high thermal stability. Examples are phthalocyanines, quinacridones, azo pigments, perylene and perinone pigments, benzimidazolone pigments, anthraquinone pigments, isoindolinone and isoindoline pigments, anthanthrone pigments, dioxazine pigments, quinophthalone pigments, diketopyrrolopyrrole pigments        additives, such as devolatilizers, flatting agents, antioxidants, tribo additives,        leveling agents, waxes for improving the scratch resistance, for example.        
For the preparation of the powder coating material, all of the constituents are first premixed in a mixer, then homogenized in an extruder or compounder at from 80 to 130° C., and finally brought to the final particle size by grinding and sieving. During the preparation of pigmented systems, it is especially important to disrupt pigment agglomerates into very finely divided form and to disperse pigment aggregates very homogenously indeed in order to obtain the optimum color strength. Nowadays this is done by introducing mechanical energy by way of the screw configuration of the extruders or compounders used, without using a dispersing aid.